Back to EveryPatent.com
| United States Patent |
5,522,808
|
|
Skalla
|
June 4, 1996
|
Surgery plume filter device and method of filtering
Abstract
A filter device and method of filtering components from a surgery plume.
The filter device is comprised of a plurality of elements which react with
one or more components of a surgery plume, such as that generated during
electrocautery or laser surgery. The filter device, particularly in
conjunction with a separate particle filter, removes cyanide,
formaldehyde, benzene, and particulates, as well as odor-causing species
and moisture from the surgery plume.
| Inventors:
|
Skalla; Randy M. (Leesburg, GA)
|
| Assignee:
|
EnviroSurgical, Inc. (Cincinnati, OH)
|
| Appl. No.:
|
198480 |
| Filed:
|
February 18, 1994 |
| Current U.S. Class: |
604/319; 95/150; 604/317 |
| Intern'l Class: |
A61M 001/00 |
| Field of Search: |
422/1,4,28,33,168,169
604/317,319
55/482,486
95/90-92,150
96/131,136
|
References Cited
U.S. Patent Documents
| 3963463 | Jun., 1976 | Huppke.
| |
| 3969479 | Jul., 1976 | Lonnes et al.
| |
| 4125589 | Nov., 1978 | deVries.
| |
| 4238461 | Dec., 1980 | Devries.
| |
| 4403611 | Sep., 1983 | Babbitt et al.
| |
| 4425143 | Jan., 1984 | Nishizawa et al.
| |
| 4443354 | Apr., 1984 | Eian.
| |
| 4604110 | Aug., 1986 | Frazier.
| |
| 4624791 | Nov., 1986 | Ferriss.
| |
| 4826513 | May., 1989 | Stackhouse et al.
| |
| 4963134 | Oct., 1990 | Backscheider et al.
| |
| 4986839 | Jan., 1991 | Wertz.
| |
| 5030423 | Jul., 1991 | Obee et al.
| |
| 5039319 | Aug., 1991 | Glass et al. | 95/150.
|
| 5047072 | Sep., 1991 | Wertz et al. | 604/319.
|
| 5108621 | Apr., 1992 | Robins.
| |
| Foreign Patent Documents |
| 0218574 | Apr., 1987 | EP.
| |
| 3135428 | Apr., 1983 | DE.
| |
| 1333635 | Oct., 1973 | GB.
| |
| 19168 | Nov., 1992 | WO.
| |
Other References
Inglis et al "Analysis of Fumes", Proc. Annual Int. Conf. IEEE Engineering
in Medicine & Biology Society, Vol. 13, 1991, p. 1759 XP 348175.
|
Primary Examiner: Green; Randall L.
Assistant Examiner: Clarke; Robert
Attorney, Agent or Firm: Wood, Herron & Evans
Parent Case Text
This is a divisional of application Ser. No. 07/851,862, filed Mar. 16,
1992, now U.S. Pat. No. 5,288,469.
Claims
What is claimed is:
1. A method of treating an airstream containing gaseous and particulate
materials from a surgery plume comprising:
directing a surgery plume airstream containing gaseous and particulate
materials including cyanide, formaldehyde, organic compounds, moisture and
odor-causing species into a container adapted to accept and exhaust an
airstream;
introducing into said container a reactive solution;
forming and breaking down a foam with said reactive solution and said
airstream in an area inside said container;
maintaining said cyanide, formaldehyde, organic compounds, and
odor-containing species contained in said airstream in said foam forming
area for a time sufficient to effect removal thereof from said airstream;
and
exhausting a treated airstream from said container.
2. The method of claim 1 wherein said airstream is directed into said
container at a rate of at least about forty SCFM.
3. The method of claim 1 further comprising passing said airstream through
a desiccant layer prior to said exhausting.
4. The method of claim 3 further comprising passing said airstream through
an activated carbon layer after passing through said desiccant layer and
prior to said exhausting.
5. The method of claim 1 wherein said airstream is directed into said
container at a rate of flow between about 55 SCFM and about 70 SCFM.
6. The method of claim 1 wherein the particulate materials of said
airstream directed into said container comprise matter formed during a
process of burning tissue, and bacteria and viruses.
7. The method of claim 1 further comprising contacting said dispersion with
bacteria and viruses in said airstream for a time sufficient to kill said
bacteria and said viruses.
8. The method of claim 1 further comprising passing said airstream through
an activated carbon layer prior to said exhausting.
9. The method of claim 1 further wherein said foam is continually formed
and broken down.
10. A method of treating an airstream containing bacteria and viruses from
a surgery plume comprising:
directing a surgery plume airstream containing bacteria and viruses at an
inlet air pressure into a container adapted to accept and exhaust an
airstream;
introducing into said container a reactive solution;
forming and breaking down a foam in an area inside said container;
maintaining said bacteria and viruses in said foam forming area for a time
sufficient to kill said bacteria and said viruses; and
exhausting a treated airstream from said container at an outlet air
pressure approximately corresponding to said inlet air pressure.
11. The method of claim 10 further comprising passing said airstream
through an activated carbon layer prior to said exhausting.
12. A method of treating an airstream containing bacteria and viruses from
a surgery plume comprising:
inducing a vacuum in a container adapted to accept and exhaust an
airstream;
directing a surgery plume airstream containing bacteria and viruses into
said container;
introducing into said container a reactive solution;
forming and breaking down a foam with said reactive solution and said
airstream inside said container;
contacting said foam with said bacteria and viruses for a time sufficient
to kill said bacteria and said viruses; and
exhausting a treated airstream from said container.
13. The method of claim 12 further wherein said foam is continually formed
and broken down.
14. A method of treating an airstream containing gaseous and particulate
materials generated from burning tissue comprising:
directing an airstream containing gaseous and particulate materials
generated from burning tissue into a container adapted to accept and
exhaust an airstream;
introducing into said container a solution reactive to at least one of the
gaseous and particulate materials in said airstream;
forming and breaking down a foam with said reactive solution and said
airstream in an area inside said container;
maintaining said gaseous and particulate materials in said airstream in
said foam forming area for a time sufficient to effect removal thereof
from said airstream; and
exhausting a treated airstream from said container.
15. The method of claim 14 further wherein said foam is continually formed
and broken down.
16. A method of treating an airstream containing gaseous and particulate
materials from a surgery plume comprising:
directing the airstream comprising said gaseous and particulate materials
into a canister having an inlet and an outlet, said inlet adapted to
receive an airstream containing gaseous and particulate materials from a
surgery plume;
passing said airstream through a series of filter members positioned inside
said canister downstream of said inlet for treating said airstream, said
series including at least one said filter member incorporating a component
reactive to cyanide and at least one said filter member incorporating a
component reactive to aldehydes;
passing said airstream through a discrete desiccant layer downstream of
said inlet and a discrete activated carbon layer downstream of said
desiccant layer; and
exhausting said treated airstream through said outlet of said canister.
Description
FIELD OF THE INVENTION
The invention relates to a filtering device, and a method of filtering, for
removing from an airstream particulates, various hazardous and odor
causing chemicals. Specifically, the invention relates to a filter device
for removing hazardous and odor causing species from an airstream
generated in an operating room, such as by the surgical application of
focused energy on tissue, as in electrocautery or laser surgery.
BACKGROUND OF THE INVENTION
It has been known for a number of years to utilize focused energy in the
form of heat or electricity to burn or scar skin and underlying tissue in
connection with the treatment of various ailments and disease. The
practice, known as cauterization, has been particularly useful for the
removal of abnormal skin growths. One drawback to the practice has been
the generation of foul-smelling materials at the site resulting from the
burning of the tissue. Fortunately, the volume of these materials was
typically relatively low due to the type of ailments treated by the
process. However, where electrocautery is used to seal blood vessels in
connection with invasive surgery, the volume of materials generated is
substantially increased.
Since the 1970's, lasers have been used in operating rooms to treat a wide
variety of ailments. As in the traditional practice of cauterization, the
laser was used to burn or sear tissue. However, because the laser was used
in larger scale invasive surgery, the amount of materials generated at the
site was substantially larger than that from traditional cauterization,
with resulting problems related to the volume of the foul-smelling
materials and the effect on operating room personnel.
The gas-generation problem has become more prevalent because in a number of
surgical applications, lasers have an advantage over conventional scalpel
cutting tools in that the laser is a more precise instrument, resulting in
less trauma to adjacent tissue. Also, because the heat generated by the
laser cauterizes the tissue as it is being cut, there is less blood loss
and the healing process is speeded along.
In operation, the laser scalpel performs its cutting function by burning a
narrow width of tissue. This process vaporizes moisture in the tissue and
creates a smoke plume consisting primarily of water vapor, but which also
includes small quantities of potentially hazardous and toxic gases,
odor-causing gases, particulate matter of 1 micron or less, and bacteria
and viruses.
This smoke generated by the laser scalpel, otherwise known as the laser
plume, creates a variety of problems for the surgical operating team. The
laser plume obscures the view of the surgeon during cutting. Further, the
plume eventually deposits a coating on the mirrors used for viewing the
cutting site. The operating room personnel also risk contracting infection
by inhaling bacteria and virus from the tissue vaporized by the laser
which are carried in the plume. The materials generated by the laser
scalpel and carried in the laser plume tend to cause headaches and nausea,
and more rarely nosebleeds and vomiting, which in certain instances have
forced the operation to be terminated due to the sickness of the
personnel. Finally, it has recently been determined that low levels of
mutagenic and carcinogenic agents such as cyanide, formaldehyde and
benzene are carried along in the plume.
The volume of the generated laser plume is a function of the power of the
laser scalpel. As higher powered lasers are used, increasing amounts of
laser plume are generated, consequently increasing the risk and discomfort
to the operating team. The major lasers used in the medical and surgical
fields utilize the lasing materials Neodymium-Yttrium Aluminum Garnet
(Nd:YAG), Carbon Dioxide and Argon.
Early attempts to address the problem of removing the laser plume involved
the use of vacuum devices fitted with an activated charcoal filter. These
early devices removed the laser plume smoke from the cutting site and
improved the surgeon's view of the site. However, the vacuum device could
not remove all of the plume generated by high energy laser scalpels. Also,
the moisture in the plume would tend to deactivate the charcoal over a
period of time. Further, the charcoal filter had little or no effect on
reducing the odor.
To meet the new requirements caused by the use of higher powered lasers,
LASE Inc., a subsidiary of U.S. Medical Corporation, Cincinnati, Ohio,
developed a smoke evacuation system incorporating an activated charcoal
filter, a moisture filter before the charcoal filter to prevent
deactivation of the charcoal filter, a high efficiency particle absorbing
filter for capturing particles as small as 0.12 micron, a larger diameter
hose to capture the increased volume of laser plume generated, and a
deodorizing cartridge to mask the odor created by the plume. One type of
evacuator unit used in laser surgery was the Lase System II, from U.S.
Medical Corporation, and discussed in U.S. Pat. No. 4,963,134 which is
incorporated herein by reference.
In the middle 1980's, clinical studies were conducted which determined that
amounts of mutagenic and carcinogenic agents such as cyanide, formaldehyde
and benzene, and also traces of compounds such as acetone, isopropanol,
cyclohexane, and toluene, are produced during the laser surgery operation.
Studies also recently determined that bacteria and viruses in the tissue
subjected to laser were carried in the active state in the plume. Smoke
evacuation systems employing only activated carbon and a particulate
filter are unable to remove the mutagenic agents, bacteria and virus
species, and the odor causing species from the plume. Rather, these
systems were only able to partially mask the odor causing species in the
plume.
SUMMARY OF THE INVENTION
It has been an object of the invention to provide a device for filtering
surgery plume such as that caused by lasers which actually removes odor
from the airstream as opposed to merely masking the odor.
It has been a further object of the invention to provide a filter device
which removes mutagenic and carcinogenic agents of the type detected in
surgery plume.
It has been yet a further object of the invention to provide a method of
removing mutagenic and carcinogenic agents and odors from surgery plume
contained in an airstream.
It has been yet a further object of the invention to provide a solution for
dispensing in a filter device which is particularly effective in removing
mutagenic and carcinogenic agents, odors, and active bacteria and virus
from an airstream incorporating a surgery plume.
It has been yet a further object of the invention to provide a filter
device for removing chemical compounds and particulates from the site of
the operation which would otherwise be harmful to operating room
personnel.
These and other objects and advantages of the invention are obtained by a
filter device for receiving an airstream having a surgery plume component
such as from laser surgery which can accept the airstream at flow rates
necessary for removing substantially all surgery plume from the operating
area, which further can eliminate or reduce to acceptable exposure limits
the known mutagenic and carcinogenic agents and odor in the surgery plume
from the airstream before it exits the device. The discussion herein will
use the term "surgery plume" to include not only the gaseous and
particulate materials generated in electrocautery and laser surgery, but
also the volatile bonding agents used in orthopedic procedures, bone
tissue particles from cutting or drilling procedures, and the like.
Important to the removal of these agents from the laser plume component of
the airstream is the incorporation of an oxidizing and surface active
solution which is dispersed inside the device through which the surgery
plume must travel. Excellent results have been obtained by dispersing the
solution in the form of a foam. Foam is generated by the effect of the air
entering the device and interacting with the solution. The contact time of
the surgery plume with the foam containing the surface active and
oxidizing component in the filter device is sufficient to break down most
of the mutagenic and carcinogenic agents and odor causing species, and to
kill the bacteria and virus in the surgery plume, thus removing these
agent from the airstream. Downstream of the foam are separate layers of a
drying agent and an activated carbon filter which collect moisture and
trap residual particulate species and stable but hazardous organic
compounds such as benzene, thus removing these agents also from the
airstream. The drying agent or desiccant, minimizes the quantity of
moisture seen by the activated carbon which would otherwise coat and
render inactive the absorbing surface of the carbon. An ultra low particle
size absorbing filter is preferably placed in-line and downstream from the
device to capture particulate matter down to 0.01 microns which would
otherwise pass through the device and be exhausted to the environment.
These and other objectives and advantages of the invention are described in
greater detail below, and are shown in the drawings in which:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of the filter cart unit shown in phantom,
which houses the filter device and interfacing equipment;
FIG. 2 is a diagrammatic top view of the filter cart unit shown in phantom,
housing the filter device;
FIG. 3 is a perspective view of the filter device with attached solution
inlet line;
FIG. 4 is a cross-sectional view of the filter device with solution
introduction port; and
FIG. 5 is a cross-sectional side view of an alternative filter device
application.
DETAILED DESCRIPTION OF THE INVENTION
The invention in its broad aspects is adapted to accept an airstream
containing gaseous and particulate materials comprising cyanide,
formaldehyde, organic compounds, odor-causing species and moisture
generated during cauterization or other treatment of animal tissue whereby
the apparatus removes the cyanide, formaldehyde, organic compounds,
odor-causing species and moisture from the airstream. The apparatus also
inactivates bacteria and virus carried along in the airstream. One such
apparatus is a filter assembly for receiving and treating an airstream
containing gaseous and particulate materials from a surgery plume
comprising a canister for retaining a plurality of filter components and
having an inlet and an outlet, the inlet for receiving the airstream which
contains the gaseous and particulate materials at a rate of flow;
introducing means for introducing an aqueous solution comprised of
oxidizing and surface active components downstream of the canister inlet;
a first porous member downstream of the introducing means for receiving
the aqueous solution and the gaseous and particulate materials, adapted to
generate a dispersion of the aqueous solution by the interaction of the
aqueous solution with the airstream through the porous member; and
activated carbon in the canister through which the airstream flows. Good
results have been obtained by placing in the canister downstream of the
first porous member a second porous member spaced from the first to create
a chamber which receives the foam.
As noted above, the surgery plume has been found to contain not only water
vapor, hydrogen cyanide, formaldehyde, benzene, odor causing species which
typically include additional aldehydes, and particulate matter formed
during the burning process, but also bacteria and viruses. Studies have
indicated that the HIV virus, among others, has been detected in the
surgery plume. It is also believed that human papilloma virus (HPV) may
also be transmitted in the surgery plume. Thus, it is important not only
that the virus component be evacuated from the surgery site, but that it
be killed before the evacuated airstream is reintroduced to the
environment. In comparing the approximate particle sizes of surgery plume
components, bacteria has particle diameters in the range of about 0.2 to
about 25 microns (10.sup.-6 meter), and the smoke components of the
surgery plume from the laser operation have particles with diameters
ranging from about 0.15 to about 8 microns, while the particle diameters
of viruses reach a minimum of about 0.05 micron. A container of oxidizing
solution through which an airstream is bubbled to remove virus components
forms bubbles which are too large in diameter to permit adequate contact
of the virus species with the oxidizing solution. It has been found that
use of a foam, which is continually being broken down and reformed by the
interaction of the airstream with an oxidizing solution containing a
surface active component in a defined space, results in sufficient contact
time with the bacteria and virus components to kill these species.
Alternatively, dispersion in the form of sprays or mists may be employed,
but the surface area of the oxidizing solution exposed to the airstream is
not as great as the foam in a canister of equal size.
The hydrogen cyanide component of the surgery plume is oxidized by contact
with the solution to form cyanate. The formaldehyde as well as any other
aldehydes present in the odor causing species become oxidized or
polymerized in the presence of the oxidizing solution as the airstream
passes through the foam layer.
The benzene component of the surgery plume is resistant to oxidation
because of its chemical stability. Nonetheless, it is removed from an
airstream by passing that airstream through a layer of activated carbon
which absorbs the benzene and other organic compounds. One drawback to the
use of activated carbon in the same system with an aqueous solution or a
moisture-laden airstream is that the moisture as it passes through the
activated carbon tends to deactivate the material and render it unable to
remove organic species such as benzene. Thus, it is necessary that a
desiccant layer be interposed between the moisture source and the
activated carbon layer to optimize the absorption ability of the carbon.
So long as the airstream passing through the activated carbon layer is of
approximately the same humidity as that of the surgery room, typically in
the range of about sixty percent to about eighty percent relative
humidity, the level of moisture is sufficiently low to maintain absorption
sites on the activated carbon layer to remove the benzene and other
organic components.
To provide further assurance that the formaldehyde and other aldehyde
components in the surgery plume are removed by the filter device, an
optional discrete porous member coated or impregnated with an aldehyde
polymerizing agent may be positioned in the filter device.
The odor causing species are removed from the airstream by contact with the
oxidizing component in the foam, and are further susceptible to removal as
the airstream passes over the desiccant and activated carbon layers,
removal being by absorption onto the surface of these layers.
The oxidizing component can be one or a mixture of a number of compounds.
Representative materials include but are not limited to sodium
hypochlorite, sodium perborate, sodium permanganate, and sodium
thiosulfate. The oxidizing agent concentration in the solution is
typically in the range of about 0.5 to about 25%, by weight.
The surface active component also can be one or a mixture of a number of
compounds. Representative materials include but are not limited to sodium
alpha olefin sulfonate, sodium lauryl dimethylamine oxide, nonylphenol
polyethylene glycol ether such as TERGITOL NP-10, and disodium oxy-bis
dodecyl benzene sulfonate. The surface active component must be
essentially inert to the oxidizing agent, yet be capable of contributing
to the foam formation of the aqueous solution containing oxidizing agent.
The surfactant concentration in the solution is typically in the range of
about 1 to about 5%, by weight.
The oxidizing solution is formed by adding the surfactant component to cold
water, then adding the oxidizing agent. The solution maintains optimum
long-term stability if the pH is at least about 10.5, typically in the
range of about 11.5 to about 12. Where the pH is very alkaline due to the
addition of the surfactant, in the range of 13 to about 14, the pH can be
lowered by the measured addition of sodium bicarbonate.
Representative desiccant materials are anhydrous calcium sulfate (4 mesh),
amorphous silica and naturally-derived zeolites based on calcium
aluminate. Activated carbon is available from Calgon, Inc., Pittsburgh,
Pa., in six mesh particle size.
As an alternative to the removal of surgery plume components in a filter
device utilizing in part an aqueous oxidizing solution, removal of the
cyanide, formaldehyde and benzene components from an airstream has also
been effected using a filter assembly without adding oxidizing solution.
This assembly comprises a canister for retaining a plurality of filter
components and having an inlet and an outlet, the inlet for receiving the
airstream containing the gaseous and particulate materials including
cyanide, formaldehyde and benzene from the surgery plume at a rate of
flow, a filter member inside the canister incorporating a component which
is reactive to at least the cyanide component, a discrete desiccant layer
inside the canister, a filter member inside the canister incorporating a
component reactive to at least the aldehyde component, and a discrete
layer of activated carbon for removal of benzene and other organic
compounds which is downstream of the desiccant layer. Instead of a foam
solution containing oxidizing and surface active components, the dry
filter assembly utilizes discrete porous members, such as pads or sponges,
coated or impregnated with oxidizing or neutralizing solutions in
combination with an aldehyde polymerizing agent incorporated onto a
discrete pad, and further retaining the discrete desiccant and activated
carbon layers for removal of cyanide, aldehydes, and benzene and other
organic compounds. The relative positions of the separate layers is not
believed to affect removal capability, except that the carbon layer
retains its activity longer if it is downstream of the desiccant layer.
The porous members in the dry filter assembly will include individual
members coated or impregnated with compounds which are reactive to
components of the surgery plume. These compounds are applied to individual
porous members by dipping the members into, or spraying the member with, a
solution of the agent, followed by drying. Alternatively, a dry powder
containing the agent can be directly applied to the pad.
The amount of compound deposited onto the porous member is a function of
the porosity and size of the member, and the concentration of the
solution. Aqueous solutions which are reactive to hydrogen cyanide which
were used to coat porous members include the following: 20% potassium
permanganate; 50% sodium hydroxide; 20% sodium dichloro-s-triazinetrione
dihydrate; 45% potassium hydroxide; 10% sodium perborate; and 20% sodium
thiosulfate. The alkaline materials listed above coated onto a porous
member retained cyanide, but did not convert the cyanide to any extent to
a less toxic material. The above percentages are to be considered as
representative only. It can be appreciated that other concentration
solutions can be used for dipping and spraying. In practice, an amount of
agent must be applied which is effective to react with the airstream
components over the period of time that the filter assembly is in
operation. Because live bacteria and virus are carried into the filter
assembly, both with the dry filter assembly and the filter assembly
utilizing the oxidizing solution, it is safer practice to dispose of the
filter assembly after each use. It has been estimated that presently the
maximum amount of time that a laser scalpel is used in a single operation
is approximately fifteen minutes. An additional safety factor of about
fifteen minutes operating time is built in, resulting in a disposable
filter assembly which would be effective in removing the gaseous and
particulate materials generated by current laser scalpels for a period of
about thirty minutes. As surgical techniques and power levels on lasers
and electrocautery knives change, the working lifetime of the disposable
filter assembly will need to also be adjusted.
A material reactive to formaldehyde and other aldehydes is available
commercially as Formalex.TM., S & S Company of Georgia, Inc., Albany, Ga.
This proprietary material removes the aldehyde component from the
airstream by polymerizing the aldehyde. This material applied to a porous
member at full strength and then dried was effective in removing
formaldehyde from the surgery plume.
In both the wet and dry filter assemblies, minimal head pressure drop is
desirable, to permit relatively high airstream flow rates with smaller
vacuum units which operate relatively quietly in the operating room
environment. The particulate matter in the surgery plume is partially
removed as the airstream flows through the multiple porous pads, desiccant
and activated carbon layers. However, remaining particulate matter down to
a particle size of 0.01 micron is removed by a separate ULPA (ultra low
particle absorbing) filter downstream of the filter assembly, prior to
exhausting of the airstream back into the operating room environment. One
such ULPA filter is manufactured by Flanders Filters.
Referring to the drawings, FIGS. 1 and 2 are schematic views of the filter
cart unit 2 which houses the filter assembly 6 and its complementary
components. Attached to the inlet port 8 of filter assembly 6 is a
flexible hose 10 with a suction tip 12 which is placed near the tissue
site where the laser surgery, electrocautery, or other gaseous or
particulate generating operation is taking place.
The filter assembly 6 is comprised of a cone portion 16 and a cylindrical
portion 18. The cone portion 16 has an inlet port 8 at one end and is
permanently attached to the cylindrical portion 18 by adhesive or heat
bond, or the like, at the other end. The cone portion 16 has a raised lip
22 with tabs 24 along a portion of the raised lip 22 which fit into and
lock with corresponding slots 28 in the filter cart unit 2 to retain the
filter assembly 6 in position.
A feed port 32 is located on cone portion 16 at the inlet port 8 to permit
introduction of an aqueous solution inside the filter assembly 6. Feed
line 36 is attached to feed port 32 and connects with pump unit 40 for
supplying a measured portion of oxidizing solution when the wet filter
assembly is being used. Pump unit 40 in turn is connected to solution
reservoir 44 outside the filter cart unit 2 via supply line 46 for
supplying the needed oxidizing solution. Alternatively, the reservoir may
be located inside the filter cart unit 2. Acceptable results have been
obtained by suspending the solution reservoir 44 above the filter cart
unit as in a plastic bag on a support such as an I.V. pole to facilitate
proper flow to the pump unit 40 and thereby into the filter assembly 6.
The pump unit 40 facilitates uniform, measured introduction of the
oxidizing solution into the filter assembly 6, and the solution flow rate
is controlled at keypad 48. However, it can be appreciated that other
types of methods of fluid introduction can be utilized, even including
direct gravity feed from an I.V. bag into the filter assembly 6 via the
feed port 32.
Flow rates of oxidizing solution are in the range of about 2.9 to about 7.3
ml/min over the course of the run, and preferably between about 3 and 5
ml/min. As noted, a peristaltic pump such as the Model 54856-070 from VWR
Scientific, Philadelphia, Pa., is useful in this application, which can
provide the desired solution flow rate by varying the tubing diameter, the
cycling time of the pump, or both. For the typical use period of about
fifteen minutes, this flow rate provides excellent foam generation without
overloading the filter assembly, as evidenced by foam appearing at the
filter assembly exhaust.
The suction applied at the surgery site through suction tip 12 is created
in a vacuum unit 50 which is connected to the exhaust side of filter
assembly 6 through connecting line 52 and gasketed fitting 56. The vacuum
unit 50 preferably generates flow rates in the range of about 35 to about
85 standard cubic feet per minute (SCFM), and more preferably between
about 55 and about 70 SCFM. A representative vacuum unit is manufactured
by Ametek, such as Model No. 116763-13. To minimize back flow from the
vacuum unit 50 particularly after the filter assembly 6 has been removed
from the cart 2 for disposal, the connecting line 52 is fitted with a
flip-up shutter door (not shown) which isolates the air system.
Residual particulates in the airstream from the surgery plume which flow
through the components of the filter assembly 6 down to 0.01 micron in
size are trapped in the particle filter 60 directly connected to the
downstream end of vacuum unit 50. After passage through particle filter
60, the airstream is exhausted to the operating room environment through
cart exhaust port 66. Power to the vacuum unit 50 and pump 40 is directly
controlled by foot switch 68 or by keypad 48.
As shown in FIG. 4, the filter assembly 6 receives solution through feed
line 36 and feed port 32 which is blown into first dispersal pad 72 by the
action of the incoming airstream as indicated by the arrow at inlet port
8. The placement of the tip of feed port 32 should be such as to obtain
good dispersion of the solution droplets. The first dispersal pad 72 is
porous and is constructed of material inert to the components of the
surgery plume and the oxidizing solution. One type of pad is manufactured
from a 60:40 blend of nylon and polyester fibers bonded with thermoplastic
resin, by Americo, Inc., Atworth, Ga., discussed in more detail below.
This pad spans the entire inside diameter of the cylindrical portion 18 of
assembly filter 6 to prevent the airstream from bypassing the pad along
the inside wall of cylindrical portion 18 and is retained in position by
tube spacers 74 on the upstream side and a bead of hot melt adhesive on
the upstream side of the pad which contacts both the pad and the inside
circumference of the cylindrical portion 18.
Downstream of the first dispersal pad 72 is a second dispersal pad 80. This
pad, like first dispersal pad 72, is secured by a bead of hot melt
adhesive on the upstream side of the pad. The pad is also manufactured by
Americo, Inc. and is discussed in more detail below. This second dispersal
pad 80 is coated or impregnated with a formaldehyde reactive component
which aids in the formaldehyde removal. An example of such a reactive
component is a material sold under the name FORMALEX.TM., available from S
& S company of Georgia, Inc., Albany, Ga. FORMALEX.TM. is a proprietary
compound which serves to polymerize aldehydes, particularly formaldehyde.
Alternatively, the second dispersal pad 80 can be uncoated.
Downstream of the second dispersal pad 80 is a filter cartridge 86 which is
secured into the cylindrical portion 18 by a flexible plastisol end cap
88. The filter cartridge 86 has a nose section 90 with a plurality of
spacer ribs 92 to deflect air along the side of the filter cartridge 86.
The filter cartridge 86 has a tubular construction with an outer layer 96
comprised of a non-woven polyester substrate media impregnated with
amorphous silica and serving as a desiccant, such as Lewcott Grade
SG-NWPE-4.0-150. The silica is mixed with a polyvinyl acetate adhesive
which is then applied to the polyester media. Inside the outer layer 96 is
a first carbon tube 98, which is comprised of two wraps of a non-woven
polyester substrate media impregnated with activated carbon ground and
mixed with a polyvinyl acetate adhesive, such as Lewcott Grade
ACF-NWPE-4.0-150. Under the first carbon layer 98 is a second carbon layer
98a, which is comprised of coal based powdered activated carbon,
regenerated cellulose, cellulosic fiber and latex binder, such as Lydall
Grade 703 carbon filter media. Under this layer is a cellulose layer 99,
comprised of cellulose media with a trace of polyamide wet strength resin,
such as Ahlstrom Grade 1278. The innermost tube in the filter cartridge 86
is a perforated tube 100 which is injection molded and made from
polypropylene, available from Crellin, Inc. As shown in FIG. 4, the entire
center length of the filter cartridge 86 is open, which serves as an
exhaust conduit for passing the airstream out of the filter assembly 6.
Structural support along the outside of the filter cartridge 86 is
provided by an outer layer of low density polyethylene extruded netting
102, such as Naltex Grade 407.
The plastisol end cap 88 which retains the filter cartridge 86 inside
cylindrical portion. 18 of filter assembly 6 is ring-shaped and secures to
the polypropylene perforated tube of the filter cartridge 86 and the
outside surface of the cylindrical portion 18 by a bead of adhesive around
the entire circumference of cylindrical portion 18. The plastisol material
is a colloidal dispersal of a vinylchloride resin and a plasticizer which
is FDA approved for use in potable water applications, such as Dennis
Chemical Grade 9233-40. This plastisol end cap 86 is sealingly connected
to the vacuum unit 50 from which the suction creating the airstream flow
through filter assembly 6 is generated. The filter assembly 6 is shown as
a discrete unit in FIG. 3.
An alternative filter assembly removes cyanide, formaldehyde and other
aldehydes and benzene from an airstream without the use of a separately
introduced oxidizing solution. As shown in FIG. 5, filter assembly 106 has
an inlet port 108 for receiving a flexible hose, such as the hose 10 shown
in FIG. 1. The filter assembly 106 is comprised of a cone portion 116 and
a cylindrical portion 118. On cone portion 116 is a raised lip 122 at the
point of friction fit connection to the cylindrical portion 118. On this
raised lip 122 are a plurality of tabs 124 for mating with slots, such as
those shown in FIG. 1 as slots 28.
Inside the cylindrical portion 118 are a variety of spaces for receiving
various spacer members, reactive members, and absorptive materials. One
material which has been used both as a spacer pad to hold a position in
the cylindrical portion, help disperse the airstream, and to serve as the
substrate for one or more chemical coatings to render the pad reactive is
a 60/40 nylon/polyester composite with a thermoplastic resin as a bonding
agent, such as that manufactured by Americo, Inc. The spaces within the
filter assembly in FIG. 5, designated I-VII, are filled with layers of
desiccant, activated carbon, impregnated or coated pads, and uncoated
spacer pads in different configurations. Where desired, one or more spaces
can be left empty. The pads are secured in the filter assembly 106 by a
bead of hot melt glue around the inside diameter of the cylindrical
portion 188. The spaces I-VII are filled with a pad coated or impregnated
with a neutralizing or oxidizing agent to remove cyanide, a pad with an
aldehyde-removing agent, such as Formalex.TM., and a layer of activated
carbon to remove benzene and other organic compounds. Typically, a layer
of desiccant is placed within the cylindrical portion 118 upstream of the
activated carbon layer. Spacer pads with no coating are used to separate
and maintain the position of the desiccant and activated carbon layers and
to help disperse the airstream, where desired.
In a typical configuration, from the upstream end, (I) is a porous uncoated
pad, followed by a porous pad coated with sodium hydroxide solution and
dried (II), a porous pad coated with FORMALEX.TM. (III), a layer of
desiccant (IV), a spacer pad (V), a layer of activated carbon (VI) and a
final spacer pad (VII).
Because the major component of the laser plume is water vapor, there is a
risk that moisture levels can rise within the filter assembly 106 to a
point where any activated carbon therein loses its activity. Thus, to
maximize the absorption time of any activated carbon, it is preferred that
a desiccant layer be located upstream of any activated carbon. It has been
found that good results can be obtained with the activated carbon at the
downstream end of the filter assembly 106, with the desiccant directly
upstream. However, it is believed that acceptable results can be obtained
even where activated carbon is located near the upstream end of the filter
assembly 106. Where the period of moisture buildup is relatively short,
the activated carbon layer can be used without the benefit of an upstream
desiccant layer. However, as expected, the working lifetime of the
activated carbon is shortened.
Operating Examples
The following detailed operating examples illustrate the practice of the
invention in its most preferred form, thereby enabling a person of
ordinary skill in the art to practice the invention. The principles of
this invention, its operating parameters and other obvious modifications
thereof will be understood in view of the following detailed procedure.
A filter assembly of the type shown in FIG. 4 was constructed having a
cylindrical portion 18 with a ten inch length and four inch inside
diameter and made from clear polyvinyl chloride to permit viewing of the
filter assembly components. Inside the assembly was an uncoated first
dispersal pad 72 and a second dispersal pad 80 coated with FORMALEX.TM..
The first dispersal pad was one inch thick and four inches in diameter and
made from a nonwoven nylon/polyester blend such as that used for
manufacturing industrial floor scrubbing pads. This particular pad
material was manufactured by Americo, Inc., Atworth, Ga., and has been
used in both wet and dry filter assemblies as a dispersal and spacer pad
and as a substrate for an agent reactive to cyanide. The nylon fiber
component of this pad has a 60 denier. The polyester fiber components have
a range of deniers of 45, 50, 100 and 300. The pad material when used in
its scrubbing application is identified as the TRUE GRIT.TM., green
cleaner pad. The second dispersal pad 80 was also obtained from Americo,
and the commercial product is identified as the TRUE GRIT.TM. tan buff
pad. The nylon fiber component has a 60 denier. The polyester fiber
components have deniers of 25, 45, 50 and 60. This second pad was also one
inch thick and four inches in diameter, and coated with FORMALEX.TM.
having a total dried weight of 8.0 grams. This pad was typically used as
the substrate for the FORMALEX.TM. coating.
An aqueous oxidizing solution of 2.5% sodium lauryl dimethylamine oxide
(30% active), 2.5% sodium alpha olefin sulfonate (40% active) and 10%
sodium hypochlorite (9.5% active) with the pH adjusted to about 11 by
addition of sodium bicarbonate was introduced through feed port 32 at a
rate of about 5.5 ml/min over the course of the run. The airstream was
conducted into the filter assembly at a flow rate of about 60 SCFM. In a
first run, the airstream was injected with E. Coli colonies and nutrient
to produce a concentration upstream of the filter of about 2.6 billion
colonies/min. over a fifteen minute period. In a second run, the airstream
was injected with Serratia Marcescens and nutrient to produce an upstream
concentration of almost one billion colonies/min. over a fifteen minute
monitoring period.
After about one minute of operation in both runs, it was observed that the
foam generated in the space between the first and second dispersal pads
was relatively coarse. Foam was also forming downstream of the second
dispersal pad between the inner wall of the cylindrical portion 18 and the
outer layer 96 of filter cartridge 86. This foam had a much finer bubble
structure, with the consistency of a shaving cream. No foam or visible
moisture escaped from the filter assembly during the runs.
Analysis of the airstream exhausted through the filter assembly showed no
detectable living bacteria. A series of control runs utilizing the same
bacteria in the same concentration without the filter showed substantial
amounts of detected living bacteria colonies.
A dry filter assembly as generally shown in FIG. 5 was constructed from a
Kraft paper-wrapped tube with a white paper outer layer and an inner
coating of paraffin wax. As with the wet filter assembly, the paper tube
cylindrical portion 18 had a four inch inside diameter and a ten inch
length. The following table shows the removal ability of various
configurations of filter components against certain materials typically
found in surgery plume. The pads were secured inside the cylindrical
portion 18 by a continuous bead of hot melt adhesive on the upstream side.
TABLE 1
______________________________________
Component
Concentration
(PPM)
Plume (Sampling every
Component Filter 2 min.)
Run Monitored Configuration Pre-filter
Post
______________________________________
Filter 1
Hydrogen I Open Cell
Cyanide Urethane
Sponge
II Green Pad 1. 7 <2
(uncoated)
III Buff Pad 2. 3.5 2
w/Formalex.TM.
IV Anhyd. CaSO.sub.4
3. 5 <2
V Green Pad 4. 7 N.D.
(uncoated)
VI Activated
Carbon
VII Green Pad
(uncoated)
______________________________________
Component
Concentration
(PPM)
Plume (Sampling every
Component Filter 5 min.)
Run Monitored Configuration Pre-filter
Post
______________________________________
Filter 2
Formalde- I Green Pad
hyde (uncoated)
II Buff Pad 1. 15 N.D.
w/Formalex.TM.
III Green Pad 2. >25 4.5
(uncoated)
IV Zeolite 3. 15 1.5
(Ca Aluminate)
V Green Pad 4. >15 4
(uncoated)
VI Activated 5. 20 3
Carbon
VII Green Pad
(uncoated)
______________________________________
Component
Concentration
(PPM)
Plume (Sampling every
Component Filter 2 min.)
Run Monitored Configuration Pre-filter
Post
______________________________________
Filter 3
Smoke/ I Green Pad Smoke was
Odor w/NaOH reduced;
II Green Pad Odor not substan-
(uncoated)
tially affected
III Zeolite
(Ca Aluminate)
IV Green Pad
(uncoated)
V Activated
Carbon
VI Activated
Carbon
VII Green Pad
(Uncoated)
______________________________________
Component
Concentration
(PPM)
Plume (Sampling every
Component Filter 2 min.)
Run Monitored Configuration Pre-filter
Post
______________________________________
Filter 1
Hydrogen I Green Pad 1. >60 26
Cyanide w/NaOH
II Green Pad 2. 58 30
w/NaOH
III Buff Pad 3. 47 20
w/Formalex.TM.
IV Zeolite 4. 45 22
(Ca Aluminate)
V Green Pad
(uncoated)
VI Activated
Carbon
VII Green Pad
(uncoated)
______________________________________
The wet filter assembly having the filter cartridge 86 positioned therein
has been found to be effective in achieving excellent contact time with
the surgery plume component by increasing significantly the surface area
through which the surgery plume must pass with minimum drop in the head
pressure across the filter assembly. It is estimated that the head
pressure drop in this filter assembly is approximately only three percent.
In contrast, testing has been conducted on a hybrid filter assembly having
the internal configuration similar to the dry filter, but with injection
of an oxidizing solution as in the wet filter. Good results were obtained
as to removal of certain particulates, odor-causing species, moisture, and
cyanide, formaldehyde, and benzene. However, the reactive agents coated
onto the porous pad or sponge tended to become blinded by the volume of
fluids inside the filter assembly, which increased the head pressure drop,
and in time decreased the filtering efficiency.
Maximum efficiency in removing the odor-causing species from the surgery
plume is observed with the wet filter assembly. Though the concentration
of suspected carcinogenic/mutagenic agents in a surgery plume can be
substantially decreased using the dry filter assembly, residual odor does
carry through.
Thus is it apparent that there has been provided, in accordance with the
invention, a filter assembly and method of filtering which fully satisfies
the objects, aims, and advantages set forth above. While the invention has
been described in conjunction with specific embodiments thereof, it is
evident that many alternatives, modifications, and variations will be
apparent to those skilled in the art in light of the foregoing
description. Accordingly, departures may be made from such details without
departing from the spirit or scope of the general inventive concept. For
example, it will be appreciated that the surgery plume would include
components found in blood and other body fluids. These components may be
found to be pathogenic and thus the plume could include blood-borne
pathogens such as those defined in 29 CFR .sctn.1910.1030.
Top